This invention relates to a defrosting control device, and more particularly, to an improved frost sensor used to control the defrost cycle of a refrigeration system. While the invention is described with particular emphasis in respect to refrigeration systems, those skilled in the art will recognize the wider applicability of the inventive concepts disclosed hereinafter.
Refrigeration systems, particularly the evaporator coils of refrigerators, air conditioning equipment or heat pump systems, are susceptible to frost accumulation during operation. Frost accumulation is undesirable in that it decreases the cooling efficiency of the system, reduces the capacity of the system, and raises operating cost. Even though its defficiencies are well known, frost accumulation and the related problem of detection have plagued refrigeration systems for a long time, and a number of methods and devices have been proposed to initiate defrost cycles for refrigeration systems. For example, timers often are employed to initiate a defrost cycle after some elapsed time period. Mechanical counters have been utilized in certain domestic appliances to initiate a defrost cycle after some preset number of door openings on the appliance. Photoelectric ice detecting devices also have been proposed for frost detecting purposes. The photoelectric detecting devices in general operate by causing radiant energy from a light source to be reflected, scattered, refracted or otherwise transmitted from the radiant energy source to a sensor, the amount of radiant energy transmitted in turn being dependent upon the frost or ice build-up of a particular sensed surface.
While it is known that frosting inhibits the efficiency of the refrigeration system and reduces the system capacity, that degradation does not occur immediately, and most systems are capable of accumulating frost for some predetermined period before efficiency begins to decrease. The problem of course, is to be able to detect that amount of frost which inhibits system efficiency, and to initiate a defrost cycle precisely when efficiency begins to decrease. In the past, frost detectors of which I am familiar have been unable to accurately measure frost growth so that they have not been able to initiate a defrost cycle precisely when that defrost is required. Defrost cycle initiation at times other than the optimum frost condition is known in the art as a false defrost cycle. False defrost cycles decrease system efficiency and increase operating costs, which defeats the very purpose of the frost detector in the first place. While the invention disclosed hereinafter employs a photo cell as the sensing device, the sensor construction is distinguishable from prior art detectors employing photo cell devices in that the detector is designed for direct placement on the coil of the evaporator of a refrigeration system. In addition, the mounting structure is adjustably mounted with respect to a tangent along the outer surface of the tubular coil structure so that the irradiating energy source and the sensor may be adjusted with respect to a line of sight tangent across the coil tube. A direct line of sight reading is maintained between the sensor and the energy source. Frost is allowed to accumulate on the tube until the frost growth itself blocks radiation transmission to the sensor. Since the sensor is a line of sight communicator, a very precise light beam source may be employed, and very small differences in frost growth detected. Those small differences in frost growth enable the detector to initiate the defrost cycle for the refrigeration system at or very near the frosting condition at which the frost begins to interfere with system efficiency. Since the detector is adjustably mounted with respect to a tangent across the coil tube, the precise desired frost condition before defrost initiation for any particular application may be obtained and set by field personnel.
One of the objects of this invention is to provide an improved frost sensor for detecting the presence of frost.
Another object of this invention is to provide a frost sensor which employs narrow line of sight communication between the radiation source and a sensor, frost growth in the application destroying the line of sight communication therebetween to trigger the defrost cycle.
Another object of this invention is to provide a frost detector which is adjustably mounted with respect to a tangent across a tubular structure on which the sensor is mounted.
Another object of this invention is to provide a low cost sensor that permits frost growth to a predetermined height with respect to the tube of an evaporator coil, and initiates the defrost cycle once that frost height is reached.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.